7793r is working on an X-drive using 4 motors on turbo gearing direct drive to small omni. This is about the same as high speed gearing with the large 4in omni wheels. Speed is a much more important factor this game, as there is no bump or aggressive pushing between robots.
2.4:1, on an x drive? Even on smaller (2.75") wheels, your drive motors will burn out if you have 4 motors on the drive, unless your robot is incredibly light. That is the equivalent of 2.33:1 on 4" wheels, slightly faster than high speed (160rpm) 393s on 4" wheels on an x drive. I’ve seen that burn out on a light Toss Up robot, and what with reaching the higher scoring areas, I doubt Skyrise robots will be as light as most Toss Up robots.
Good for you that you have all aluminum. Our aluminum plan is still being drafted and waiting to be launched this summer. So i would vote for a 1:1.6 robot with four motors and try to keep it lighter than 20 lbs.
Wow. Amazing. That would be approximately 1:2.33345. Actually slightly faster than 4inch wheel high speed. How heavy do you plan to make your bot? I would say under 15 lbs?
240rpm8.6(circumference of small omni)=2064in/min
160rpm12.6(circumference of large omni)=2016in/min
100rpm*(5/3)*12.6(5:3 is the gear ratio we used in toss up)=2100in/min
As you can see higher speed=less torque (it was faster to calculate this way)
and the 4 motor drive we used for Toss Up NEVER burned out! 
So the torque remains relatively equal throughout the 3 calculations above.
The third config we used has the most energy loss because of the use of gears.
This leads me to believe it will perform the same as the high torque 5:3 large omni config we used (the reason for 5:3 was because we also had a 3:5 transmission for pushing) but when on speed, the motors never burnt out once. Since there will be almost no pushing in Skyrise, it will be fine to just use speed on your robot.
Actually since you are using an x-drive it is naturally faster with a ratio of 1:sqrt(2)
So approximately 1:1.4
Just going to say, a turbo X drive will NOT work out on 4 motors unless your robot is under 10 pounds and even then…
We had an 11 pound robot with a 6 motor X drive at 1.6, not even 2.4, and it had issues before we got to the bump. We could have made that work, but that’s 6 motors and it’s not geared turbo. You are going to stall out.
I was actually thinking that a transmission drive might work really well. We’d have a sensor near the middle of the tray telling us when there were 3 or more cubes in our robot, and the robot would automatically change over to speed. The torque might be important to not get pushed around, and the speed is definitely important in the last 15 seconds or so when everyone is running around trying to get possession.
–
George
Yeah we won’t actually start building till probably late August. A lot of CAD this summer
Anyways the more I think about it the more I like the 20 lb limit that you suggested. Though we have some unique ideas for our design that would substantially cut our weight. We might be able to get under 15 lbs…maybe? Lightweight lifts will be key this year.
This is where we got our robot slimdown idea: building scissor lift out of metal bars rather than c channels. That saves approximately a half of the weight.
Never seen a scissor lift like that before :eek: BEAUTIFUL
Yup… i am still CADing it and optimizing it. We plan to do a six or seven stage lift. Our initial plan is: AURA shifting x drive, metal bar scissor lift and our unique intake idea;)
People should pay attention to this post.
The wheel circumference is a variable in ground speed. It is somewhat silly to discuss what gearing you’re going to use without also mentioning what wheel diameter you’re using. Are you using 5" wheels? 2.75" wheels? Big difference.
I think even on the small wheels he will still have stalling issues at that gear ratio with only 4 motors.
I disagree completely, while speed is an important factor it is also more important to be able to hold your ground when in a push Battle over a post. I plan on gearing my drive for torque with six motors after what I discovered at worlds and watching a certain team. The abilty to control the other robots by overpowering them is just as important if not more than speed.
I disagree completely. While it is nice to push teams around, it will be completely unnecessary as there are 10 regular towers for your to score on in 120sec plus your alliances skyrise. I don’t know why you would need to play defense as most of your time will be building your skyrise and scoring your 22 cubes on the 10 towers (and floor goals). Defense will not be as important as Toss Up. The only time I think you will need a 6 motor 1:1 drive is, well, never. 1:1 is too slow with the 4" wheels, and if you have the 3.75" or 2.75" wheels, that’s even slower.
That’s just my view Skyrise, but I’m sure there are other views 
EDIT:
I guess I’ll chime in on what a good gear ratio would be for drive’s. I personally will be using either a :
- 1:1.6 Internally Geared drive with 4" wheels (20.096in/rev)
- 1:3 Chained drive with 2.75" wheels (25.905in/rev)
I might use something in between, but we shall see. I need to further develop my design and strategy 
There is no point in playing defense, if you push someone they’ll just move on to the next post and outscore you because they’re faster
So much this. Also people need to take into account your robot weight. Setting aside the fact that it will effect your actual performance speed, robot weight will greatly effect if you “brown out” your motors. I know a lot of teams like to design their drives before anything else, but if you do this, I would make sure you design with the ability to change your drive speed easily as it will be tough to know how much your robot weighs until after you at least roughly design everything. You could also design your other subsystems at the same time or before so you can be more exact with your drive design.
The man quoted above a couple years ago made a fantastic mechanical design calculator that is very useful. It includes calculators for single speed drives, 2-speed drives, arms, elevators, etc. I think it would be great to see more teams utilize these kind of calculations in your design.
I would also suggest taking the time to not only use this calculator, but look at the formulas that are used for excel to make the calculations so you can learn how some of the results are found.
JVN’s Mechanical Design Calculator
Even the best teams in FRC use this calculator or their own very similar all the time when designing their robots every season.
-Nick
I say speed. This is a game of speed this isn’t a game like gateway in which involved a lot of defence and strategy gaming. This is a game of which ever make the most points. I think that in the first few competitions you won’t even see other robots touching each other. But always expect a surprise in the Worlds. hahaha
So how many wheels are people planning on having on each side? And what wheels I’m what configuration? I plan to build an elevator lift and might have a 6wheel drive for a good COG balanced on a center wheel? Still considering wheel type though. Any ideas?